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Description

This search identifies a high frequency of file deletions relative to the process name and process ID. Such events typically occur when ransomware attempts to encrypt files with specific extensions, leading Sysmon to treat the original files as deleted as soon as they are replaced with encrypted data.

  • Type: Anomaly

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-03-05
  • Author: Teoderick Contreras, Splunk, Steven Dick
  • ID: 45b125c4-866f-11eb-a95a-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1485 Data Destruction Impact
Kill Chain Phase
  • Actions On Objectives
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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`sysmon` EventCode IN ("23","26") TargetFilename IN ("*.cmd", "*.ini","*.gif", "*.jpg", "*.jpeg", "*.db", "*.ps1", "*.doc", "*.docx", "*.xls", "*.xlsx", "*.ppt", "*.pptx", "*.bmp","*.zip", "*.rar", "*.7z", "*.chm", "*.png", "*.log", "*.vbs", "*.js", "*.vhd", "*.bak", "*.wbcat", "*.bkf" , "*.backup*", "*.dsk", "*.win") NOT TargetFilename IN ("*\\INetCache\\Content.Outlook\\*") 
| stats count, values(TargetFilename) as deleted_files, min(_time) as firstTime, max(_time) as lastTime by user, dest, signature, signature_id, Image, process_name, process_guid 
| rename Image as process 
| where count >=100 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_high_file_deletion_frequency_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_high_file_deletion_frequency_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • EventCode
  • TargetFilename
  • dest
  • user
  • Image
  • ProcessID
  • _time

How To Implement

To successfully implement this search, you need to ingest logs that include the deleted target file name, process name, and process ID from your endpoints. If you are using Sysmon, ensure you have at least version 2.0 of the Sysmon TA installed.

Known False Positives

Users may delete a large number of pictures or files in a folder, which could trigger this detection. Additionally, heavy usage of PowerBI and Outlook may also result in false positives.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
72.0 90 80 Elevated file deletion rate observed from process [$process_name$] on machine $dest$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 2